There is still so much missing information about this engine build.

You never stated the measured compression ratio. Tell us about the 0.015 over pistons, who made it and what's the final compression distance. What is the cranking cylinder pressure? Because you you milled the heads a bunch, had them "rebuilt", and put a Whiplash cam in it suggests to me that this was a budget build and you put bandaides on it to make up for the low compression.

Does it have headers? If you are using exhaust manifolds, that is not a good cam choice.

Mustang or Dyno Jet dyno?

If that is 304 RWHP on a Mustang dyno for what I'm guessing this build is, that's not bad. And, IMO, 304 RWHP is a nice performing street car. 304 RWHP you should be able to drive it to the track and pull directly into the staging lane and run a 13.00 at 105 mph with a street tire/stock converter 60 ft of 2.0 sec.

HP numbers from any dyno, chassis or engine is just the first step. I prefer an engine dyno, because you can get more data to decide if it needs tuning, and or what is right or not right with the combo. While nothing stops you from having exhaust gas temps, 02's, fuel flow, BSFC, etc. nobody usually takes the time to set up an engine on a chassis dyno. To tune your combination I would want to know cranking compression, to get a handle on dynamic compression ratio, and exhaust temps, along with 02 readings to see how efficient combustion is. One HP per cubic inch is what I use as a reasonable goal on a mild engine with bolt on's as you describe.

What is the actual compression ratio? Very low I’m betting. A buddy of mine has a couple motorhome 440 blocks and both have huge bevels on the bore/deck.

I dyno'd my 78 Ramcharger, it ran perfectly fine, edelbrock 750 cfm carb, performer intake, dual exhaust, it made a blistering 121 rwhp. At 300 rwhp, that's quite the improvement you've made actually. For reference, my SRT10 ram with no mods made 355-ish rwhp.

Some friends in town have a chassis dyno in their shop.
It’s a dyno jet. They’re on there 2nd one.
The first one was the intertia style that had the heavy large diameter rollers.

Probably around 15 years ago they had a 69 Charger on it.
Flat top 440, SD intake, Demon 850, ootb RPM heads, 1-7/8” headers, MP 509 cam, 10” converter, 3.91’s.
Ran fine, felt pretty hot driving it around.
Made around 285hp to the wheels. The guy was all upset.

Took it to the track and it went 11’s.

I’ve seen a lot of that kind of thing that really make me scratch my head.


The new Dyno Jet they have has smaller rollers and uses an eddy current type of absorber instead of inertia....... so you can actually load the motor prior to making a “pull”, along with being able to set the accel rate.

I haven’t seen that one in action yet.

Friends have tried to get me to put my car on a chassis dyno at one of the events we attend.

I have no interest. To me they are a tuning tool and nothing more.

The only numbers that matter to me are the ones at the dragstrip. Even then, mph is what is relevant to hp. You can have crap for tires and chassis and a lousy e.t. but still get a close idea from weight and mph of what the engine is making.

low rear axle gears and loose converters can have an adverse effect on a chassis dyno outcome.

I'm curious on these .015 over pistons also. SO....custom pistons yet you still need steel shim gaskets to and to shave the heads to get the compression up?

After watching a few videos with cars on hub dynos, making simulated 1/4 runs as they go thru the gears........ I can see where that could be pretty helpful.

https://m.facebook.com/590227367683050/videos/522722568322028/

Oh..... and yeh...... that thing sounds bad a$$!!!

I saw a S/C Corvette on the dyno when I worked at a race shop. 406 small block with a glide. 6500 stall and 5.38 gears. Dyno'd 440 at the wheels. Went 8:50@163 at the track. Dyno's are tuning tools, nothing more.

That sounds a lot nicer what do the dyno sheets say ?
Any measurements made on that dyno are not the same as at the track with the hood on forcing air into the carbs would be
I wouldn't trust those results to be same as they would be at the track
Two things I look at and trust the most for tuning is the spark plug and the time slip

The 224 smaller drum is still inertia, the 224xlc is inertia and eddy current. I have the xlc now , I use to have a 248 , the large drum version. The stack has to be matched to the machines drum weight, if you use someone elses stack(dyno computer module), you'll get whacked readings. The 248 actually had loading via the modulation of the air brakes(locomotive brake shoes), if the brakes were acting up or setup wrong, it caused low readings, mine would flutter the air solenoid, it stopped when I fixed the cable shielding.Dynojets are calibrated on the inertia weight so that no matter where you dyno a car, if the same correction is used the number spit out should be pretty close to the same anywhere on a given car strappped down in a consistent manner on any dynojet. I keep notes on cars I dyno that I know are coming back.
Strapping the car down incorrectly will put a dent in the power. The less angle on the straps the better, but some people put angle in to load the tries up if the knurling is worn on the drums. I opted to build my own deck for the dyno, a longer version so that trucks and longer cars would still have less steep angle from the rear strap points.

FWIW...my cuda only made around 630 RWHP on the local dynojet. I was surprised (figured it'd be higher, of course), but didn't really care since the car had already run 9.50s at 140+ mph at 3800 lbs.

Use the dyno as a tuning tool and nothing more.

My friends bought both of their dynos new from Dyno Jet...... complete with whatever electronics were needed to go along with them.

Dyno's are just a tuning tool, fact, however here in the uk I don't know what dyno's were used but I know of 2 cars that were tested and both those cars weight/mph@the track showed pretty much spot on dyno numbers. Whether this was just luck I'm not sure.

One of which was the car I crewed on last year. Dyno'd@695fwhp at EDF......weight@the line 3800lbs.+/- a few either way with the slicks, best mph last year was 130.14 on a perfect day with no headwind, plenty of 129+runs......thats 680hp, this is through the same carb/timing as dyno run but with all ancillaries and a full exhaust system with an air cleaner, basically as it drives on the street.

wallace has it with 680fwhp/3800lbs>

60 Foot E.T. : 1.44 Seconds
1/8 Mile E.T. : 6.52 Seconds
1/8 Mile Trap Speed : 104.22 MPH
1/4 Mile E.T. : 10.34 Seconds
1/4 Mile Trap Speed : 130 MPH
its gone a best of 10.35 with a best 60 of 1.431

so not saying dyno's are the be all they are certainly not, weight/mph is your dyno just sometimes at least here they showed pretty accurate numbers twice that I know of.

Dyno results through an automatic can sometimes be misleading, especially with a higher stall converter. Some produce realistic results, some read super low.

That power may be dead on but we need more info because you’ve got a lot missing. Does the car feel strong to you? If you really want to know if it makes the power it should take it to the track and see what the trap speed is.

If you did not buy a higher compression piston for it then the results sound about right.

Still should be checked, you have to send your stack in every once in awhile for a chip that expires, also your software disk is serialized as well with the dyno particulars.
My old and new dyno produced pretty much the same numbers when the same car was run on both.

Why? The dyno is measuring power at the wheels, how it’s transmitted is irrelevant at that point.

Yes Pacnorthcuda but with an accurate weight and a couple of runs to get a trap speed, the horsepower can be calculated and that will be accurate. His 60 foot times and traction are irrelevant. It would either confirm or call into question what the dyno is telling him